Current UI designs have business constraints that just can't allow for much change. The user is not the customer, the user can't be bothered to invest time to l

Current UI designs have business constraints that just can't allow for much change. The user is not the customer, the user can't be bothered to invest time to learn as there are multiple apps competing for their attention, if the user is familiar with some UI design you can't give him a completely different design regardless of how much better it is and so on. In spaces where the business considerations are different (aviation, medical devices, mature open source projects, etc) the UI is pretty good for the target users.